The present invention relates to an electron generating source including a housing and a cathode which is contacted by a high voltage generator.
In particle accelerators particles are accelerated by electrical fields produced in suitable structures. The energy gain per unit length, which is related to the cost and structure of the accelerators, is limited by the maximum possible field intensity in these structures and, in the case of circular accelerators, additionally by the maximum field intensity of the bending magnets.
Acceleration rates which are greater by several orders of magnitude can be expected with collective accelerators in which space charge fields of as great a density as possible are utilized for the acceleration. One type of collective accelerator which has been proposed and which is presently the subject of research, is the electron ring accelerator in which the desired high acceleration fields are generated by the formation of a ring of electrons of a very high charge density. Such an accelerator is described in a paper by H. Schopper in Physical Reports No. 24, pages 201,255 (1968).
In order to fully realize the advantages of the electron ring accelerator, the maximum field intensity at the edge of the ring must be about 100 MV/m. This resultas in requirements for special performance levels for the electron ring accelerator as well as requirements for the injector needed for the accelerator, e.g. an electron current of at least 400 A at an emittance of 0.1 cmrad with an energy of 2 MeV and a pulse duration of several nanoseconds. Similar beam requirements also exist for electron beam pumped high energy lasers.
In a known arrangement, such as the Febetron Type 705 manufactured by Field Emission Corp., a 160-stage Marx generator with a stored energy of 800 J is accomodated in a pressure tank and furnishes an output pulse of 2.3 MV at a maximum load voltage of 35 kV to 400 .OMEGA. at a half value of .about. 50 nsec. The diode employed, which is composed of a cathode electrode - anode electrode system, includes a molten glass tube, 24 tungsten tips as the field emission cathode, a titanium window of a thickness of 25 .mu. or 70 .mu. as the anode, and an internal magnet which focusses the electrons through the titanium window.
The beam quality of this diode is such that at an emittance of 0.1 cmrad, of the 6 kA total current only 40 to 50 A, or 30 A, can be utilized. After an average of 100 or 500 pulses, depending on the titanium window thickness, the titanium window is shot through and the glass is damaged by the electron bombardment.
The geometric arrangement of the cathode with respect to the anode, the internal solenoid being also at anode potential, also requires a distribution of the electrical field which leads to wide angles and thus to poor beam quality. Therefore, the internal solenoid and thus the magnetic focussing are useless. Furthermore, the titanium window leads to bulging of the beam as a result of multiple dispersion.